PHOTOGRAPHIC ATLAS OF SOCKEYE SALMON SCALES 



BY KENNETH H. MOSHER, Fishery Biologist 



BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY 

 SEATTLE, WASHINGTON 98102 



ABSTRACT 



Photographic plates of sockeye salmon scales, with ex- 

 planatory' text, illustrate in detail the variations in scale 

 features in this species. These illustrations of zones of fresh- 

 water and ocean growth (and of complete scales) can be used 

 as: (1) standards to which scales under study may be re- 



ferred for determination of age and race, (2) guides in choos- 

 ing scale characters for racial and other studies, and (3) aids 

 in the training of scale scientists. Examples of regenerated, 

 resorbed, and other atypical scales are also shown. 



Sockeye salmon (Oncorhynchus nerka) is the 

 most valuable species of Pacific salmon in Northi 

 America and has been the subject of scientific 

 study since the 1870's. Most of the extensive re- 

 search for the INPFC (International North 

 Pacific Fisheries Commission) by Canada, Japan, 

 and the United States now is directed toward this 

 species. Many of these projects use data obtained 

 from study of the scales of sockeye salmon. 



Sockeye salmon spend their early lives in fresh 

 water, migrate to the North Pacific Ocean, and 

 finally return to their natal streams to spawn and 

 die. The gi'o\\i;h zones formed on the scales record 

 the growth of each individual fish. The fresh- and 

 salt-water zones differ from each other in appear- 

 ance. The zones can reveal the number of years 

 that the fish spent in each environment ; they also 

 divulge the year in which the fish was hatched and 

 the year it migi'ated to sea. Scale features have 

 been used in age studies of sockeye salmon since 

 1910 (Gilbert, 1913). Recently, scale features 

 have also been used in racial studies to determine 

 the origin of fish taken at sea (Krogius, 19.58; 

 Kubo, 1958; Kubo and Kosaka, 1959; Henry, 

 1961; Mosher, Anas, and Liscom, 1961; Anas. 

 1963 ; Mosher, 1963 ; and Anas. 1964) . 



No detailed information has been published, 

 however, on how to interpret the scales. The pur- 

 pose of this atlas is to show the features of sock- 

 eye salmon scales in detail so that workers can in- 

 terpret the scales they are working with to pro- 

 vide the data required in their studies. 



A section on the use of the atlas in age studies 

 and for describing scale features follows the illus- 

 trations of the scale features. 



MATERIALS AND METHODS 



Scientists of BCF (Bureau of Commercial 

 Fisheries) have examined many thousands of 

 sockeye salmon scales in recent years to supply 

 inforaiation to the United States Section of 

 INPFC. From these thousands I have selected 

 certain scales to illustrate the variations in scale 

 characters among fish. Variations may be genetic 

 or environmental, or both, but generally many 

 of the differences in the characters of scales are 

 linked to geographic localities ; therefore, a study 

 of these variations offers a means of determining 

 the mainland (racial) origin of fish taken beyond 

 their natal streams. 



For scale studies, workers of the research 

 agencies of the INPFC (Fisheries Agency of 

 Japan, Fisheries Research Board of Canada, and 

 BCF) collect scales from the side of the fish as 

 shown in Mosher, 1963. The "preferred scale" is 

 in the second scale row above the lateral line in 

 the diagonal scale row downward from the pos- 

 terior edge of the dorsal fin. If this scale is missing 

 on both sides of the fish, a scale is taken as close 

 as possible to the preferred position, but not from 

 the lateral line or the first row above or below the 

 line. 



The plates of the atlas are made from negative 



Published November 1968. 



FISHERY BULLETIN: VOL. 67, No. 2 



243 



